This invention relates to a device for material identification of the invention, with particular application to inspection of freight or baggage for one or more types of material.
X-ray systems used in freight and baggage screening use a broad spectrum X-ray generator to illuminate the item to be screened. A detector array on the opposite side of the item is used to measure the intensity of X-ray flux passing through the item. Larger systems may have the option to have two or more X-ray sources so as to collect two or more projections through the cargo at the same time. X-Ray screening systems use the differential absorption of the low energy and high energy X-rays to generate a very coarse classification of the screened material, and then use this coarse classification to generate a “false color” image for display. A small number of colors—as few as 3 in most existing systems—are used to represent material classification.
Traditional detectors are arranged in a 1×N array comprising, most typically, phosphorus or Si—PIN diodes, to enable an image of N rows and M columns, captured row by row as the item passes through the scanning system. An image resolution of 1-2 mm can be achieved with around 2,000 detectors in the array. However, these systems simply produce an image based on the integrated density (along the line of sight between X-ray source and detector) of the contents of the item being screened. Two different detector arrays are used to generate a single image, one to generate the high energy image and the other to generate the low energy image. This gives an improved estimate of integrated density and a rudimentary ability to identify items as either organic or metal. In a screening application, where the objective is to identify ‘contraband’ or other items of interest, the range of material which incorrectly falls into the ‘contraband’ classification is large. As such, a skilled operator may be required to identify potential threat material from the large number of false alarms.
There is a need for improved freight and baggage screening systems.